This invention relates to an apparatus and method for transporting, metering, mixing, and applying the solid and liquid ingredients for concrete at a job site.
In the construction of certain concrete structures such as swimming pools, it is necessary to apply concrete to the sides and bottoms of the swimming pool. Conventional practice is to mix the basic ingredients of concrete to form a slurry and then to spray the slurry from a hose under sufficient pressure against the surface to be covered. An accelerator agent is injected as the concrete leaves the spray nozzle to cause it to harden almost immediately. The concrete spray product produced is sometimes termed "gunite."
Because swimming pools and similar structures requiring the use of this gunite approach are usually constructed at sites remote from conventional concrete plants, the logistics of concrete preparation are important both for economic and technical reasons. A variety of machines have been developed to aid in remote-site application of gunite. While generally satisfactory for their intended purposes, problems remain in the application of gunite to swimming pool construction applications.
A principal problem has been the operator's lack of control over the composition of the gunite mixture during the application process. In some cases, the basic concrete mixture was mixed at a central plant, trucked to the remote site, and then loaded into an applicator unit. The use of a slurry premixed at the central plant deprived the operator of the applicator unit of the ability to vary the composition of the concrete on the job site to match its consistency, hardening rate and other characteristics to the different requirements of different application situations found on-site in constructing a swimming pool.
In other cases, the ingredients were trucked to the remote site unmixed and then added to a mixer by laborers working at the direction of the operator. Here the mixture could be varied on-site, but imprecisely and with considerable lag in the composition of the applied gunite. In yet other cases, there has been an attempt to provide automated mixing of the ingredients, as where separate bins are filled with controlled amounts of the ingredients and then mixed. This approach has the inherent limitation of producing batches rather than a continuous flow of mixed concrete, with the result that the operator cannot readily alter the composition on short notice and for short periods.
Another problem with previous on-site application methods has been initial set up of the equipment and adjustment of the different proportions of the ingredients to obtain the mix necessary for a concrete slurry having the properties desired. This can result in initial production of unsatisfactory slurry which cannot be used and must be wasted before the proportions have been adjusted to obtain a mix of the desired characteristics.
An associated problem is the need for an economical, self-contained vehicle upon which all storage, mixing, pumping, and spraying functions can be centralized. Other machines for applying gunite have often required a variety of separate pieces of apparatus, including mixing trucks, central plant, applicator units, and power sources. This approach is uneconomical in that capital costs are high and several operators may be required for the separate pieces of machinery. It is also inconvenient and unsightly when operations are conducted in a residential neighborhood.